Feeling Sleep when you lie down

Hi Just wondering could someone help me, my boyfriend is experiences feelings of nausea when he goes to bed at night. It would happy about twice a week. He get's the feeling when he lies down of a watery mouth, nausea and weak. He did go to the doctor and they tested him for diabetes and it came back all clear. He would have good health, 6ft, 11 stone, age 33, he coaches rowing.

He has a high metabolism, would it have anything to do with that? He said it sometimes happens if he is hungry ~ and it stops him for eating as he's feeling so sick. He ate loads yesterday and it still happened. I was thinking maybe a food intolerance test?

The doc told him he was very healthy so its a little unusual.